Consider refactoring to make libytdlr available to be used elsewhere

[hasezoey]

Consider refactoring libytdlr functionality to be able to published to crates.io for use by other crates (aside from this binary).

Notes:
This would be quite a undertaking as much stuff is currently hardcoded (ex #9) and only meant for consumption with the binary (like archive integration or recovery).

re #18

[hasezoey]

Both crates are now published to crates.io and libytdlr is useable outside of the ytdlr binary, though there are likely still improvements that could be done.

For example:

• add some default impls for the DownloadOptions trait.
• move some gen_archive functions over to the lib and provide them as possible defaults
• generally improve the documentation